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(130) Elektra Delta - on the stability of the new third moonlet
(2023-07-01) Valvano, G. [UNESP]; Oliveira, R. Machado [UNESP]; Winter, O. C. [UNESP]; Sfair, R. [UNESP]; Borderes-Motta, G.; Universidade Estadual Paulista (UNESP); Eberhard Karls Universität Tübingen; Universidad Carlos III de Madrid; Kiruna
The aim of this work is to verify the stability of the proposed orbital solutions for the third moonlet (Delta) taking into account a realistic gravitational potential for the central body of the quadruple system (Alpha). We also aim to estimate the location and size of a stability region inside the orbit of Gamma. First, we created a set of test particles with intervals of semimajor axis, eccentricities, and inclinations that covers the region interior to the orbit of Gamma, including the proposed orbit of Delta and a wide region around it. We considered three different models for the gravitational potential of Alpha: irregular polyhedron, ellipsoidal body, and oblate body. For a second scenario, Delta was considered a massive spherical body and Alpha an irregular polyhedron. Beta and Gamma were assumed as spherical massive bodies in both scenarios. The simulations showed that a large region of space is almost fully stable only when Alpha was modelled simply as an oblate body. For the scenario with Delta as a massive body, the results did not change from those as mass-less particles. Beta and Gamma do not play any relevant role in the dynamics of particles interior to the orbit of Gamma. Delta's predicted orbital elements are fully unstable and far from the nearest stable region. The primary instability source is Alpha's elongated shape. Therefore, in the determination of the orbital elements of Delta, it must be taken into account the gravitational potential of Alpha assuming, at least, an ellipsoidal shape.
The influence of a close secondary star on the planetary formation: The case of γ cephei b
(2023-07-01) Camargo, B. C.B. [UNESP]; Kley, W.; Winter, O. C. [UNESP]; Universidade Estadual Paulista (UNESP); Universität Tübingen
The formation of planets around a single star is a complex process that depends on many parameters. Planetary systems with a secondary star too close to the primary star can significantly complicate the process. In this work, we explored the formation of γ Cephei b, a giant planet located in a close binary system, using a hydrodynamic approach. We tested different parameters for the discs and protoplanet in an attempt to reproduce the observed features. We found that in situ formation can reach the observational mass of the planet. Both isothermal and radiative disc conditions exhibited similar planetary evolution. However, our results demonstrated a high planetary eccentricity. To understand this behaviour, we applied secular theory to the γ Cephei system. We found that the system can reproduce the observational and simulated values of eccentricities.
The dynamics of co-orbital giant exomoons - applications for the Kepler-1625 b and Kepler-1708 b satellite systems
(2023-04-01) Moraes, R. A. [UNESP]; Borderes-Motta, G.; Winter, O. C. [UNESP]; Mourão, D. C. [UNESP]; Universidade Estadual Paulista (UNESP); Bioengineering and Aerospace Engineering Department; Swedish Institute of Space Physics
Exomoons are a missing piece of exoplanetary science. Recently, two promising candidates were proposed, Kepler-1625 b-I and Kepler-1708 b-I. While the latter still lacks a dynamical analysis of its stability, Kepler-1625 b-I has already been the subject of several studies regarding its stability and origin. Moreover, previous works have shown that this satellite system could harbour at least two stable massive moons. Motivated by these results, we explored the stability of co-orbital exomoons using the candidates Kepler-1625 b-I and Kepler-1708 b-I as case studies. To do so, we performed numerical simulations of systems composed of the star, planet, and the co-orbital pair formed by the proposed candidates and another massive body. For the additional satellite, we varied its mass and size from a Mars-like to the case where both satellites have the same physical characteristics. We investigated the co-orbital region around the Lagrangian equilibrium point L4 of the system, setting the orbital separation between the satellites from θmin = 30◦ to θmax = 90◦. Our results show that stability islands are possible in the co-orbital region of Kepler-1708 b-I as a function of the co-orbital companion's mass and angular separation. Also, we identified that resonances of librational frequencies, especially the 2:1 resonance, can constrain the mass of the co-orbital companion. On the other hand, we found that the proximity between the host planet and the star makes the co-orbital region around Kepler-1625 b-I unstable for a massive companion. Finally, we provide TTV profiles for a planet orbited by co-orbital exomoons.
Imbalanced classification applied to asteroid resonant dynamics
(2023-01-01) Carruba, V. [UNESP]; Aljbaae, S.; Caritá, G.; Lourenço, M. V.F. [UNESP]; Martins, B. S. [UNESP]; Alves, A. A. [UNESP]; Universidade Estadual Paulista (UNESP); Division of Space Mechanics and Control
Introduction: Machine learning (ML) applications for studying asteroid resonant dynamics are a relatively new field of study. Results from several different approaches are currently available for asteroids interacting with the z2, z1, M1:2, and ν6 resonances. However, one challenge when using ML to the databases produced by these studies is that there is often a severe imbalance ratio between the number of asteroids in librating orbits and the rest of the asteroidal population. This imbalance ratio can be as high as 1:270, which can impact the performance of classical ML algorithms, that were not designed for such severe imbalances. Methods: Various techniques have been recently developed to address this problem, including cost-sensitive strategies, methods that oversample the minority class, undersample the majority one, or combinations of both. Here, we investigate the most effective approaches for improving the performance of ML algorithms for known resonant asteroidal databases. Results: Cost-sensitive methods either improved or had not affect the outcome of ML methods and should always be used, when possible. The methods that showed the best performance for the studied databases were SMOTE oversampling plus Tomek undersampling, SMOTE oversampling, and Random oversampling and undersampling. Discussion: Testing these methods first could save significant time and efforts for future studies with imbalanced asteroidal databases.
Assessing the spin-orbit obliquity of low-mass planets in the breaking the chain formation model: a story of misalignment
(2023-06-01) Esteves, Leandro [UNESP]; Izidoro, André; Winter, Othon C [UNESP]; Bitsch, Bertram; Isella, Andrea; Universidade Estadual Paulista (UNESP); Rice University; Max-Planck-Institut für Astronomie
The spin-orbit obliquity of a planetary system constraints its formation history. A large obliquity may either indicate a primordial misalignment between the star and its gaseous disc or reflect the effect of different mechanisms tilting planetary systems after formation. Observations and statistical analysis suggest that system of planets with sizes between 1 and 4 R has a wide range of obliquities (∼0-30°), and that single- and multiplanet transiting have statistically indistinguishable obliquity distributions. Here, we revisit the 'breaking the chains' formation model with focus in understanding the origin of spin-orbit obliquities. This model suggests that super-Earths and mini-Neptunes migrate close to their host stars via planet-disc gravitational interactions, forming chain of planets locked in mean-motion resonances. After gas-disc dispersal, about 90-99 per cent of these planetary systems experience dynamical instabilities, which spread the systems out. Using synthetic transit observations, we show that if planets are born in discs where the disc angular momentum is virtually aligned with the star's rotation spin, their final obliquity distributions peak at ∼5° or less, and the obliquity distributions of single- and multiplanet transiting systems are statistically distinct. By treating the star-disc alignment as a free-parameter, we show that the obliquity distributions of single- and multiplanet transiting systems only become statistically indistinguishable if planets are assumed to form in primordially misaligned natal discs with a tilt' distribution peaking at ≥10-20°. We discuss the origin of these misalignments in the context of star formation and potential implications of this scenario for formation models.
The Santa Filomena meteorite shower: Trajectory, classification, and opaque phases as indicators of metamorphic conditions
(2023-05-01) Tosi, Amanda; Zucolotto, Maria Elizabeth; Andrade, Diana Paula; Winter, Othon Cabo [UNESP]; Mourão, Daniela Cardozo [UNESP]; Sfair, Rafael [UNESP]; Ziegler, Karen; Perez, Pablo Daniel; Suarez, Sergio; Ornellas, Iara Deniz; Zurita, Marcelo; Mendes, Julio Cezar; Kellner, Alexander Wilhelm; Wolff, Wania; Universidade Federal do Rio de Janeiro (UFRJ); Universidade Estadual Paulista (UNESP); Eberhard Karls Universität Tübingen; University of New Mexico; Centro Atomico Bariloche (CONICET); Brazilian Meteor Observation Network
On August 19, 2020, at 13:18—UTC, a meteor event ended as a meteorite shower in Santa Filomena, a city in the Pernambuco State, northeast Brazil. The heliocentric orbital parameters resulting from images by cameras of the weather broadcasting system were semimajor axis a = 2.1 ± 0.1 au, eccentricity e = 0.55 ± 0.03, and inclination i = 0.15o ± 0.05. The data identified the body as an Apollo object, an Earth-crossing object with a pericenter interior to the Earth's orbit. The chemical, mineralogical, and petrological evaluations, as well as the physical analysis, followed several traditional techniques. The meteorite was identified as a H5-6 S4 W0 ordinary chondrite genomict breccia. The large amount of metal in the meteorite made a metallographic evaluation based on the opaque phases possible. The monocrystalline kamacite crystals suggest a higher petrological type and the distorted Neumann lines imply at least two different shock events. The absence of the plessite phase shows that the meteorite did not reach the highest shock levels S5 and S6. The well-defined polycrystalline taenite is indicative of petrologic types 4 and 5 due to the conserved internal tetrataenite rim at the boundaries. The presence of polycrystalline taenites and the characteristics of the Agrell Effect suggest that the Santa Filomena meteorite did not reheat above 700°C. The absence of martensite confirms reheating temperatures <800°C and a slow cooling rate. The Ni contents and sizes of the zoned taenite particles indicate a slow cooling rate ranging from 1 to 10 K Myr−1.
Optimum, Suboptimal and Solar Sailing Orbital Maneuvers for a Spacecraft Orbiting the Earth
(2023-02-01) Meireles, Lucas Gouvêa; Gomes, Vivian Martins [UNESP]; Prado, Antônio Fernando Bertachini de Almeida; Melo, Cristiano Fiorilo de; National Institute for Space Research (INPE); Universidade Estadual Paulista (UNESP); RUDN University; Universidade Federal de Minas Gerais (UFMG)
The present research performs numerical studies to search for the best maneuvers, from the point of view of minimum time, to make adjustments in the semi-major axis, eccentricity and inclination of a spacecraft traveling around the Earth. For those maneuvers, low thrust propulsion is used under optimal and sub-optimal assumptions, to verify the main differences in terms of transfer time. In addition, solar sail dynamics is used. The spacecraft is assumed to have a propulsion with a fixed magnitude and that the control is based on choosing the direction of the propulsion. It is found that optimal control gives the minimum transfer time, while sub-optimal control restricted the control to follow a predescribed function, which is assumed to be a constant or linear function in time. Finally, solar sails present themselves as an option where fuel is a critical factor, given their much longer maneuver duration, but with a zero fuel consumption. The numerical-analytical modeling of optimization methods developed in this study can break any type of symmetry in the solutions. In turn, they can increase their energetic efficiency. The present research compares those results in detail, in particular looking at the transfer time in all cases studied.
Optimization of artificial neural networks models applied to the identification of images of asteroids’ resonant arguments
(2022-12-01) Carruba, V. [UNESP]; Aljbaae, S.; Caritá, G.; Domingos, R. C. [UNESP]; Martins, B. [UNESP]; Universidade Estadual Paulista (UNESP); National Space Research Institute (INPE)
The asteroidal main belt is crossed by a web of mean motion and secular resonances that occur when there is a commensurability between fundamental frequencies of the asteroids and planets. Traditionally, these objects were identified by visual inspection of the time evolution of their resonant argument, which is a combination of orbital elements of the asteroid and the perturbing planet(s). Since the population of asteroids affected by these resonances is, in some cases, of the order of several thousand, this has become a taxing task for a human observer. Recent works used convolutional neural network (CNN) models to perform such task automatically. In this work, we compare the outcome of such models with those of some of the most advanced and publicly available CNN architectures, like the VGG, Inception, and ResNet. The performance of such models is first tested and optimized for overfitting issues, using validation sets and a series of regularization techniques like data augmentation, dropout, and batch normalization. The three best-performing models were then used to predict the labels of larger testing databases containing thousands of images. The VGG model, with and without regularizations, proved to be the most efficient method to predict labels of large datasets. Since the Vera C. Rubin observatory is likely to discover up to four million new asteroids in the next few years, the use of these models might become quite valuable to identify populations of resonant minor bodies.
Low Thrust Propelled Close Approach Maneuvers
(2022-09-01) Ferreira, Alessandra F. S. [UNESP]; Elipe, Antonio; De Moraes, Rodolpho V. [UNESP]; Prado, Antônio F. B. A.; Winter, Othon C. [UNESP]; Gomes, Vivian M. [UNESP]; Universidade Estadual Paulista (UNESP); Universidad de Zaragoza-UNIZAR; Divisão de Pós-Graduação; RUDN University
The study of orbital maneuvers in space missions is a very important problem in astrodynamics. One of the options is the use of a “gravity assisted” maneuver, which is a technique where a spacecraft passes close to a celestial body and uses the gravity of this body to change its trajectory. This approach trajectory has symmetry with respect to the periapsis line when observed from a reference frame fixed in the approached body. There is also a more complex maneuver, when the passage by the celestial body is combined with the application of propulsion, either to give extra energy to the spacecraft or to help to satisfy other constraints required by the mission, like passing by a giving point or region in space. The main object of this study is to measure the efficiency of the application of a continuous thrust combined with the “gravity assisted” maneuver. The effect of this combination is analyzed using maps that give the energy variation of the spacecraft as function of the parameters related to the maneuver. This analysis is made from the point of view of the variation of energy of the spacecraft with respect to the main body of the system. The continuous thrust is applied in the different regions of the trajectory to evaluate the effects of the locations of the thrusting arcs in the variations of energy. The effects of the variations of the direction of the thrust are also studied. This type of combined maneuver may be used to give extra energy to the spacecraft and keeping control of the trajectory during the close approach to better position the spacecraft to complete the mission.
Searching for Orbits for a Mission to the Asteroid 2001SN263 Considering Errors in the Physical Parameters
(2022-09-01) de Almeida Junior, Allan Kardec; Mescolotti, Bruna Yukiko Pinheiro Masago; Chiaradia, Ana Paula Marins [UNESP]; Gomes, Vivian M. [UNESP]; de Almeida Prado, Antonio Fernando Bertachini; Divisão de Pós-Graduação; Universidade Estadual Paulista (UNESP); RUDN University
The main goal of this paper is to search for orbits that can be used in the Brazilian proposed Aster mission. This mission is under study and its objective is to use a spacecraft to observe the system 2001SN263, which is a triple asteroid system. With respect to the two-body problem (spacecraft and the main asteroid), the symmetries of the orbits are broken by the oblateness of the main body of the system, the solar radiation pressure, and the gravitational attraction of the two moons of the main body. Additionally, the masses of these two moons have errors associated with their predicted values, which reinforce the asymmetry and require extra effort to maintain the observational objectives of the mission. The idea is to find orbits that remain for some time observing the three bodies of that system, even if the physical parameters of the bodies are not the ones expected from observations made from the Earth. This is accomplished by studying the effects of errors in all the physical properties of the three asteroids in the trajectories described by a spacecraft that is orbiting this system. Several important and useful trajectories are found, which are the ones that can observe the desired bodies, even if the physical parameters are not the expected ones. To express our results, we built time histories of the relative distances between each of the asteroids and the spacecraft. They are used to select the trajectories according to the amount of time that we need to observe each body of the system. In this way, the first objective of this research is to search for trajectories to keep the spacecraft close to the three bodies of the system as long as possible, without requiring orbital maneuvers. The errors for the masses of the two smaller and lesser known bodies are taken into consideration, while the mass of the most massive one is assumed to be known, because it was determined with higher precision by observations.
Genetic optimization of asteroid families’ membership
(2022-09-08) Lourenço, M. V.F. [UNESP]; Carruba, V. [UNESP]; Universidade Estadual Paulista (UNESP)
Asteroid families are groups of asteroids with a common origin, such as prior collisions or the parent body’s rotational fission. In proper [a, e, sin(i)] element domains, they are generally observed using the hierarchical clustering technique (HCMs), but the method may be ineffective in high-density regions, where it may be unable to separate near families. Previous works employed a different technique in which nine different machine learning classification algorithms were applied to the orbital distribution in proper elements of 21 known family constituents for the goal of new members’ identification. Each algorithm’s optimal hyper-parameters for every family were extensively investigated, which proved to be a time-consuming and repetitive procedure. Herein, we used a genetic algorithm-based tool to identify the most optimal machine learning algorithm for the same studied asteroid families as an alternative to the originally utilized parameter search mode. When compared to the same evaluative metrics utilized in the previous machine learning application study, the precision values of the new genetic machine learning algorithms have been consistently comparable, demonstrating that this alternative technique can be satisfactorily efficient and fast.
Deflecting an Asteroid on a Collision Course with Earth Using a Powered Swing-By Maneuver
(2022-08-01) Chagas, Bruno S. [UNESP]; Prado, Antonio Fernando Bertachini de Almeida; Winter, Othon Cabo [UNESP]; Universidade Estadual Paulista (UNESP); Peoples’ Friendship University of Russia (RUDN University); National Institute for Space Research (INPE)
The deflection of potentially dangerous asteroids has been treated with great intensity and has gained more and more attention in scientific research. Different techniques are developed over the years. Among these techniques, we found the kinetic impact deflection technique to be the most viable at the moment. In this work we address the kinetic impact deflection technique, but in a scenario where we have a short time to deflect an asteroid that will collide with Earth. For this, we also use a maneuver similar to a powered gravity-assisted maneuver with Earth in a previous passage to change the trajectory of the asteroid to avoid the collision. We apply this technique in three scenarios: (i) impulse before the close encounter, (ii) impulse during the close encounter, and (iii) impulse after the close encounter. We observe that some trajectories are symmetric with respect to the line Sun–Earth, and others are asymmetric. We show that, using this technique, it is possible to change the trajectory of the asteroid, even in a short period, to avoid the collision without using a large variation of velocity in the orbit of the asteroid.
2001 SN263-the contribution of their irregular shapes on the neighbourhood dynamics
(2022-09-01) Valvano, G. [UNESP]; Winter, O. C. [UNESP]; Sfair, R. [UNESP]; Machado Oliveira, R. [UNESP]; Borderes-Motta, G.; Universidade Estadual Paulista (UNESP); Eberhard Karls Universität Tübingen; LeganCrossed D sign©s
The first proposed Brazilian mission to deep space, the ASTER mission, has the triple asteroid system (153591) 2001 SN263 as a target. One of the mission's main goals is to analyse the physical and dynamical structures of the system to understand its origin and evolution. This work aims to analyse how the asteroid's irregular shape interferes with the stability around the system. The results show that the irregular shape of the bodies plays an important role in the dynamics nearby the system. For instance, the perturbation due to the (153591) 2001 SN263 Alpha's shape affects the stability in the (153591) 2001 SN263 Gamma's vicinity. Similarly, the (153591) 2001 SN263 Beta's irregularity causes a significant instability in its nearby environment. As expected, the prograde case is the most unstable, while the retrograde scenario presents more stability. Additionally, we investigate how the solar radiation pressure perturbs particles of different sizes orbiting the triple system. We found that particles with a 10-50 cm radius could survive the radiation pressure for the retrograde case. Meanwhile, to resist solar radiation, the particles in prograde orbit must be larger than the particles in retrograde orbits, at least one order of magnitude.
Machine learning applied to asteroid dynamics
(2022-08-01) Carruba, V. [UNESP]; Aljbaae, S.; Domingos, R. C. [UNESP]; Huaman, M.; Barletta, W. [UNESP]; Universidade Estadual Paulista (UNESP); Division of Space Mechanics and Control; Universidad tecnológica del Perú (UTP)
Machine learning (ML) is the branch of computer science that studies computer algorithms that can learn from data. It is mainly divided into supervised learning, where the computer is presented with examples of entries, and the goal is to learn a general rule that maps inputs to outputs, and unsupervised learning, where no label is provided to the learning algorithm, leaving it alone to find structures. Deep learning is a branch of machine learning based on numerous layers of artificial neural networks, which are computing systems inspired by the biological neural networks that constitute animal brains. In asteroid dynamics, machine learning methods have been recently used to identify members of asteroid families, small bodies images in astronomical fields, and to identify resonant arguments images of asteroids in three-body resonances, among other applications. Here, we will conduct a full review of available literature in the field and classify it in terms of metrics recently used by other authors to assess the state of the art of applications of machine learning in other astronomical subfields. For comparison, applications of machine learning to Solar System bodies, a larger area that includes imaging and spectrophotometry of small bodies, have already reached a state classified as progressing. Research communities and methodologies are more established, and the use of ML led to the discovery of new celestial objects or features, or new insights in the area. ML applied to asteroid dynamics, however, is still in the emerging phase, with smaller groups, methodologies still not well-established, and fewer papers producing discoveries or insights. Large observational surveys, like those conducted at the Zwicky Transient Facility or at the Vera C. Rubin Observatory, will produce in the next years very substantial datasets of orbital and physical properties for asteroids. Applications of ML for clustering, image identification, and anomaly detection, among others, are currently being developed and are expected of being of great help in the next few years.
Identifying the population of stable ν6resonant asteroids using large data bases
(2022-08-01) Carruba, V [UNESP]; Aljbaae, S; Domingos, R. C [UNESP]; Huaman, M; Martins, B [UNESP]; Universidade Estadual Paulista (UNESP); National Space Research Institute (INPE); Universidad Tecnológica Del Perú (UTP)
Large observational surveys, like those that will be conducted at the Vera C. Rubin Observatory, are expected to discover up to one million new asteroids in the first year of operation. This will more than double the data base of known asteroids. New methods will be needed to handle the large influx of data. Here, we tested some of these new approaches by studying the population of asteroids on stable orbits inside the ν6 secular resonance. This resonance is one of the strongest mechanisms for destabilizing the orbits of main-belt bodies and producing Near-Earth Asteroids. Yet, stable orbital configurations where the asteroid pericenter is either aligned or anti-aligned with that of Saturn exist inside the resonance. The population of stable ν6 resonators is now the largest population of asteroids in stable orbits inside a secular resonance. Here, we obtained the largest sample of asteroids' proper elements ever used. Clustering methods and the use of machine learning algorithms permitted the identification of the known asteroid families crossed by the ν6 resonance and of two entirely new groups: the Tiffanykapler and the 138605 QW177 families. The Tiffanykapler family is the first young asteroid family ever found in a linear secular resonance, with an age of 3.0 ± 1.2 My and an ejection velocity field parameter of $V_{\mathrm{ EJ}} = 15^{+6}_{-3}$ m s-1. We identify a population of high-eccentricity objects around the Tina family that may be the first example of an asteroid family 'resonant halo'.
Gravitational perturbations correlated with the asteroid kinetic impact deflection technique
(2022-12-01) Chagas, B. S. [UNESP]; Prado, A. F.B.A. [UNESP]; Winter, O. C. [UNESP]; Universidade Estadual Paulista (UNESP); RUDN University Miklukho-Maklaya; INPE: National Institute for Space Research
This paper presents the use of the kinetic impact technique to deflect asteroids that may present some risk of collision with Earth. Within the work to be developed here, we intend to evaluate in more detail the possibility to deflect the orbit of the asteroid 101955 Bennu by applying variations in its velocity (Δ v) at different positions along its orbital period and measuring effects of close encounters with planet Earth. We will see that, in a relatively long period of time, the asteroid has several close encounters with the planet, thus suffering a natural gravitational perturbation. With the application of the impulses, the relative distances change, causing variations in the energy of the asteroid and a large variation in the relative distance between the asteroid and Earth over a long period after the impulse. We present results related to the magnitude of the impulse applied, which is important because its defines the mass and velocity of the impactor to be considered. Then, we mapped the positions of the impulses along a period of the orbit of the asteroid. We finish by explaining what happens to the orbit of the asteroid during the periods of gravitational perturbation, since the close encounters amount to “Swing Bys” that intensify the variations of the relative distances between the bodies after the impulse is applied.
Dynamics around the binary system (65803) Didymos
(2021-10-18) MacHado Oliveira, R. [UNESP]; Winter, O. C. [UNESP]; Sfair, R. [UNESP]; Valvano, G. [UNESP]; Moura, T. S. [UNESP]; Borderes-Motta, G.; Universidade Estadual Paulista (UNESP); Universidad Carlos Iii de Madrid
Didymos and Dimorphos are primary and secondary, respectively, asteroids who compose a binary system that make up the set of Near Earth Asteroids (NEAs). They are targets of the Double Asteroid Redirection Test (DART), the first test mission dedicated to study of planetary defense, for which the main goal is to measure the changes caused after the secondary body is hit by a kinect impactor. The present work intends to conduct a study, through numerical integrations, on the dynamics of massless particles distributed in the vicinity of the two bodies. An approximate shape for the primary body was considered as a model of mass concentrations (mascons) and the secondary was considered as a massive point. Our results show the location and size of stable regions, and also their lifetime.
Chaos identification through the auto-correlation function indicator (ACFI)
(2021-10-05) Carruba, Valerio [UNESP]; Aljbaae, Safwan; Domingos, Rita C. [UNESP]; Huaman, Mariela; Barletta, William [UNESP]; Universidade Estadual Paulista (UNESP); National Space Research Institute (INPE); Universidad Tecnológica Del Perú (UTP)
Close encounters or resonances overlaps can create chaotic motion in small bodies in the Solar System. Approaches that measure the separation rate of trajectories that start infinitesimally near, or changes in the frequency power spectrum of time series, among others, can discover chaotic motion. In this paper, we introduce the ACF index (ACFI), which is based on the auto-correlation function of time series. Auto-correlation coefficients measure the correlation of a time-series with a lagged duplicate of itself. By counting the number of auto-correlation coefficients that are larger than 5% after a certain amount of time has passed, we can assess how the time series auto-correlates with each other. This allows for the detection of chaotic time-series characterized by low ACFI values.
Milliarcsecond Astrometry for the Galilean Moons Using Stellar Occultations
(2022-01-01) Morgado, B. E.; Gomes-Júnior, A. R. [UNESP]; Braga-Ribas, F.; Vieira-Martins, R.; Desmars, J.; Lainey, V.; D'Aversa, E.; Dunham, D.; Moore, J.; Baillié, K.; Herald, D.; Assafin, M.; Sicardy, B.; Aoki, S.; Bardecker, J.; Barton, J.; Blank, T.; Bruns, D.; Carlson, N.; Carlson, R. W.; Cobble, K.; Dunham, J.; Eisfeldt, D.; Emilio, M.; Jacques, C.; Hinse, T. C.; Kim, Y.; Malacarne, M.; Maley, P. D.; Maury, A.; Meza, E.; Oliva, F.; Orton, G. S.; Pereira, C. L.; Person, M.; Plainaki, C.; Sfair, R. [UNESP]; Sindoni, G.; Smith, M.; Sussenbach, E.; Stuart, P.; Vrolijk, J.; Winter, O. C. [UNESP]; Observatório Nacional/MCTI; Laboratório Interinstitucional de E-Astronomia - LIneA; Sorbonne Paris Cité; Universidade Estadual Paulista (UNESP); Federal University of Technology - Paraná (UTFPR/DAFIS); Universidade Federal do Rio de Janeiro (UFRJ); Institut Polytechnique des Sciences Avancées IPSA; Université Lille; INAF-IAPS; International Occultation Timing Association (IOTA); International Occultation Timing Association/European Section; Trans-Tasman Occultation Alliance (TTOA); JAXA; California Institute of Technology; Universidade Estadual de Ponta Grossa (UEPG); Observatório SONEAR; Nicolaus Copernicus University; Chungnam National University; Chungbuk National University; Universidade Federal do Espírito Santo (UFES); NASA Johnson Space Center Astronomical Society; SPACE; CONIDA; MPC Code W73; MIT; ASI; Eberhard Karls Universität Tübingen; Willemstad; Space and Nature Aruba Foundation
A stellar occultation occurs when a Solar System object passes in front of a star for an observer. This technique allows the sizes and shapes of the occulting body to be determined with kilometer precision. In addition, this technique constrains the occulting body's positions, albedos, densities, and so on. In the context of the Galilean moons, these events can provide their best ground-based astrometry, with uncertainties in the order of 1 mas ( 1/43 km at Jupiter's distance during opposition). We organized campaigns and successfully observed a stellar occultation by Io (JI) in 2021, one by Ganymede (JIII) in 2020, and one by Europa (JII) in 2019, with stations in North and South America. We also re-analyzed two previously published events: one by Europa in 2016 and another by Ganymede in 2017. We then fit the known 3D shape of the occulting satellite and determine its center of figure. This resulted in astrometric positions with uncertainties in the milliarcsecond level. The positions obtained from these stellar occultations can be used together with dynamical models to ensure highly accurate orbits of the Galilean moons. These orbits can help when planning future space probes aiming at the Jovian system, such as JUICE by ESA and Europa Clipper by NASA. They also allow more efficient planning of flyby maneuvers.
Explaining mercury via a single giant impact is highly unlikely
(Oxford Univ Press, 2022-08-18) Franco, P. [UNESP]; Izidoro, A.; Winter, O. C. [UNESP]; Torres, K. S. [UNESP]; Amarante, A. [UNESP]; Natl Observ; Universidade Estadual Paulista (UNESP); Rice Univ; Ctr Fed Educ Tecnol Minas Gerais CEFET
The classical scenario of terrestrial planet formation is characterized by a phase of giant impacts among Moon-to-Mars mass planetary embryos. While the classic model and its adaptations have produced adequate analogues of the outer three terrestrial planets, Mercury's origin remains elusive. Mercury's high-core mass fraction compared to the Earth's is particularly outstanding. Among collisional hypotheses, this feature has been long interpreted as the outcome of an energetic giant impact among two massive protoplanets. Here, we revisit the classical scenario of terrestrial planet formation with focus on the outcome of giant impacts. We have performed a large number of N-body simulations considering different initial distributions of planetary embryos and planetesimals. Our simulations tested the effects of different giant planet configurations, from virtually circular to very eccentric configurations. We compare the giant impacts produced in our simulations with those that are more likely to account for the formation of Mercury and the Moon according to smoothed hydrodynamic simulations. Impact events that could lead to Moon's formation are observed in all our simulations with up to similar to 20 per cent of all giant impacts, consistent with the range of the expected Moon-forming event conditions. On the other hand, Mercury-forming events via a single giant impact are extremely rare, accounting for less than similar to 1 per cent of all giant impacts. Our results suggest that producing Mercury as a remnant of a single giant impact that strips out the mantle of a differentiated planetary object with Earth-like iron-silicate ratio is challenging and alternative scenarios may be required (e.g. multiple collisions).

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